Receiving system



Patented Sept. 26, 1933 'y RECEIVING SYSTEM Rene A. Braden,Merchantville, N. J., assignor to Radio Corporation of America, acorporation of Delaware Applicationy January 9, 1932.

Serial No. 585,647

claims.` (c1. 25o-'2.0)

My present invention relates to electrical wave receiving systems, andmore particularly to novel methods of, and means for, amplifying theamplitude of the carrier wave of intelligence modulated carrierenergywith respect to the side bands of such carrier energy. l

It has been pointed out in my co-pending application, Serial No. 585,646filed January 9, 1932, that in the receptionof modulated carrier energythere exists various situations where it is extremely desirable toeffect amplification of the carrier amplitude with respect to side bandVat the receiving pointrso as to bring the carrier up to normal amplitudeat the detector input. (2) Selective carrier fading and general signalfading in short wave reception resulting from natural phenomena may becorrected by separating the carrier wave from the side bands, andarnplifying the carrierfrom sub-normal amplitude to normal amplitude. YY

(3) The production of harmonics in the output of the detector, which iscaused by a high degree of modulation of4 carrier wave, may beconsiderably minimized by elevating the carrier amplitude from normal tosuper-normal value in order to reduce the degreeof modulation of thecarrier wave. y

Various arrangements are disclosed in my said (zo-pending applicationfor `attaining the aforementioned objects.V l One of the arrangementsshown in the said application discloses the amplification of -thelcarrier wave from sub-normal amplitude to normal` amplitude in aseparating path which includes a carrier frequency oscillator, selectivefading beingcompensated for by this arrangement. Furthermore, it hasbeen shown in the aforementioned application that the va- 50 riousarrangements'disclosed therein Acould be successfully employed forreducing the degree of modulation of the carrierA wave, and therebyminimizing the production of harmonics in the detector output circuit ofa radio receiver. Y In the present application I have disclosed adtionedcarrier amplification is effectedto great Yembodying one form of thepresent invention,

ditional arrangements for effecting increase of carrier amplitude withrespect to side bands, for the purposes described above, andparticularly for reducing the amount of harmonics produced in thedetector output circuit of a receiver.

Accordingly, it may be stated that it is one of the main objects of mypresent application to provide a method of separating the carrierwave ofreceived modulated carrier energy from its Y side bands, treating theseparated carrier wave in such aV manner with respect to the side bandsthatthe carrier amplitude is elevated from its original value, theamplitude elevation being accomplished'in a path including a carrierfrequency oscillator. v

Another important object of the present invention is to provide a methodof rectifying modulated carrier energy with a minimum production ofharmonics in the detector output circuit, Vthe collected carrier energybeing diverted through' two paths, one of the paths including adistorting `75 v detector,"'thev outputs of both paths being combinedin'such a manner that distortion produced inthe first path issubstantially compensated for by distortion produced in the second path.

VStill other objects of the present invention are 30 "toimprovegenerally the efciency of radio reception, and to `particularlyprovide a radio' receiver wherein collected modulated carrierenergy isdivertedV into two paths, one of thepathsincluding means forcompensating for an undesiralB5 vvble characteristic existing in theenergy in the rst path thus resulting in a receiver which is not onlycapable ofreducing detector distortiondue to harmonic production in thedetector output to a great extent, but isalso capable ofreliable re- Vception of signal venergy wherein the carrier is received at subnormalamplitude.

The novel features which I believe to be `characteristic of my inventionare set forth in particularity in the appended claims, the inventionitself,

however, as to both its organization and method of operation will bestbe understood by reference Fig. 2 diagrammatically shows anotherembodiment of the invention, Y

Fig. 3 shows still another form of the-invention in diagrammatic manner.

Referring now to -the accompanying drawing Y1.1,

of side bands transmitted at full amplitude, `andA a carrier wave atmuch reduced amplitude, or a carrier wave at normal amplitude.

The reception method shown in AFigfl is-capable of compensating fordisadvantages inherent Ain the reception of carrier energy wherein thecarrier amplitude has either of theaforementioned two values. It hasalready been pointed out that detection of signal energy whereinthe'carrier is collected .at sub-normal amplitude results in distortion,while detection .of signal energy wherein .the carrier exists atnormalamplitude may result iin the .production of harmonics'in the .detectoroutputcircuitlbecause of .a high degree of modulation .of -the carrierwave,

Thelreception method in `Fig/r1, accordingly, comprises apath foramplifying the carrier wave independently .of its associated side bandsto normal or super-normal amplitudeas desired. The construction andoperation of .the arrangement shown vin Fig. 1 will be explained inconnection with the reduction of the degree .ofy modulation of the`carrier wave. The detector ci'rcuit'of the receiving arrangementincludes an Kelectron discharge device 2 arrangedfor grid bias detectionby .means of .a bias source C, the anode'of the device being .energizedfroma source B. The input ofthe detectortube includes .a tuning element,asa variable condenser 3', andthe detector receives energy, throughacoupling Mgfrom a multi-stage .radio Yfrequ`ency'-.amplifier 4 '.wh'osefinputincludes a'tuning device,.su'ch.as a .variable condenser 5, fortheselectionlof the desired carrier wave frequency. The input ofthefradiofrfequency .amplifier 4, is coupled, as at M1, to the source of signal.energy. The output of .the detector AEmay be amplified by the usualaudiofrequency amplifier 6, and then utilized in any conventionallmanner, asby Vhead phones, a loud speal'senior' the"like.Y I Itliswellknown that.rectificationpf modulated .signals produces not only audio frequencycurrents of the original vmodulation frequency, ybut alsosecond, andhigher harmonics, as well assum frequencies. The amount of extra.frequencies .produced in the detector'output. depends on the degree ofmodulation ofthe carrier wave. By reducingthe degree of modulation,.theamount of harmonics produced in the detector output will be`considerably Vminimized with resulting improved detection. Toaccomplish this reduction of the 'degree ofmodulationga path is providedbetween the vamplifier 4 andthe detector input, the vpath includinga-synchronized oscillator, conventionally shown and designated by thereference lnumeral V'7, the oscillator being tuned, asby va -variablecondenser 8,^approximately tothe-frequency of the carrier wave. Y

Theoscillator isiheld synchronized .by coupling to the outputof-.theamplifier 4. Itisto .beunderystood that `theportion of the ,pathleading tothe coupling point M3 is connectedto .the..outputof4the-amplifier 4. The rsynchronizedoscillator .'7 is not shown in itsstructural details, since any type Vafl-oscillator lwell knownto thosekskilled in-the art may be employed. lCurrent from the oscillator 7 isfed into the detector 2 with the output of the amplifier 4.

The oscillator current constitutes an addition to the carrier frequencycurrent, and in fact reduces the degree of modulation. The oscillatorcurrent :is fed through a suitable 'phase-.shifting device,

.2. For'simplicityoVOperatiOn, the tuning devices 3, 5 and 8 may bearranged for uni-control by a singlemechanism 9. c

It should .be .obvious from the aforegoing .ex-

Vpla'nation of .the reception method showninfFig. l

that proper design tof the oscillator "7 will result in supplyingoscillator current of carrier .frequency in such amount that 4theoriginal Vcarrier wave amplitude'is changed from sub-normal amplitude tonormal amplitude, or evenffrom sub-normal:- 4amplitude to super-normalamplitude 'for purposes already referred to in detail.V

InFig. 2 there is shown another embodiment of :the lpresent 'inventionwherein .a circuit 4for `increasing carrier amplitude lisdisposed'between the'usual radio frequency amplifier, andthe detectorinput. The circuit'shown in Fig.2'is identical With that shown in'Fig. 1except 'for the viact that thecarrier requencyosc'illator 7 'is disposedtector Zsothat the energy from theamplifier 4 vis transmitted Vtothedetector input through the oscillator. 'The detector 'circuit `isarrangedfor grid'leak detection Vin 'this figure'instead o'f lfor gridIbias detection, and has energyl impressed upon it vfor detectionthrough 'the couplingMz from the output Acircuit of theicarrierfrequencyoscillator which includes the tube 11).

cuitfl lA source'B supplies energy for vthe anode of `.the loscilaltortube 10 through' a radio' 'frequency choke coilll, the Yu'sualblockingcondenserv 1-2 being disposed between 'the' source B Vand the coupling'transformer primary "I3, itbeingunderstood that thelinductance coill3`iis-con- `betweenthe amplifierV 4'and theinput of the ',dem0 nected inseries with theeed backlcoill'. 'The `latter coil 'is inductivelycoupled wltlrthe coupling transformer .secondary coil '15 disposeiiinvthe input circuit ofthe'oscillator 10:

Thevcarrier frequency oscillator actually'com- 'prises' anamplifierhavingfeedback'coupling 'sufflcient 'to produce oscillations,the famplier 'being Ysynchronized for loscillatiorrfat the :camzm wavefrequency by carrierwave';oumentlfed-'into it from the amplifier4.`IYhe.side.'-fbands:arefam lplifled, .and passed onv .to :the 'detector.which :also

receives a. large :carrier vsfrequencyvoltage rom .the oscillatingtubel.. It mill thus ;he seenthat the .arrangement shown :in Eig.2rcompris :a method .for increasing carrier;amplitudeiniagpath'identical .with the-path rthrough @Whichthe -side 'bands aretransmitted, fthe; transmission 4path .in-

lective, so that theamplification .of'jthemarrier is very much greaterthan that of the side bands.

fili) The arrangements shown in Fig. `2 can clearly be employed forattaining any of the three objects noted heretofore, and is clearly`adapted to reduce the degree of modulation of the carrier wave so as todiminish harmonic production in the output of the detector circuit.

In Fig. 3 there is shown still another form of the present inventionwherein after collection of modulated carrier energy at a source 1, and4arnplification at radio frequency at4, the amplified energy is divertedinto two paths, part of the output of the amplifier 4 being transmittedthrough a detector circuit, including the tube 2 arranged for grid biasdetection in the usual manner. The input circuit of the detector tube 2includes a tuning device, vas a variable condenser 3, and is coupled, asat M2, to the output of the amplifier 4. The output of the detector tube2 is coupled, as at M4, by means of an audio frequency transformer tothe input circuit of an audio frequency amplifier, not shown.

The aforementioned second path through which the output of the amplifier4 is diverted includes a second detector circuit provided with a tube 2arranged for grid bias detection in the usual manner, the `input circuitof the tube 2 being tuned by the variable condenser 3', the cot.- plingtransformer M5 transmitting energy from the output of the amplifier 4 tothe input of the detector tube 2. In order to reduce the carrieramplitude in the path including the detector tube 2', any conventionalarrangement may be employed. For purposes of illustration, such a deviceis shown as comprising a resonant circuit which includes an inductancecoil 20 shunted by a variable condenser 21, the inductance coil 20 beingcoupled to the secondary inductance coil 22 of the coupling transformerM5.

The resonant circuit including the coil 20 and condenser 2l is sharplyresonant to the carrier wave frequency, while the resonant input circuitof the tube 2 is arranged for broad tuning by inserting a resistor 23therein in series between the coil 22 and the condenser 3. The tuningcondensers 3, 21, 3', are arranged for uni-control, as at 24, whereby atresonance the sharply tuned circuit including the inductance 20 and thecondenser 21 will absorb energy at carrier frequency from the inputcircuit of the detector tube 2' thereby effectively reducing the carrieramplitude.

The output circuit of the tube 2' is coupled to the input of the audioamplifier through an audio frequency transformer coupling M6, theprimary coil 25 of which coupling is wound in a manner opposite to thatof the primary coil of the audio frequency transformer M4. The detectedoutputs of tubes 2 and 2 are combined so that the energy from the outputof tube 2' subtracts from the combined energies. The strength of theoutput of tube 2 is adjusted, as 1n the input circuit thereof by usingthe sharply tuned absorbing circuit 20, 21 so that the amount ofcombination frequency and harmonics is substantially the same asproduced in the output of A detector tube 2.

The fundamental frequency in the output of tube 2' will, of course, besmaller than in the output of detector tube 2. Thus, subtracting theenergy produced in the output of tube 2 from that produced in the outputof tube 2 will re move a large part of the extra frequency currents,leaving undistorted currents which are then amplified and utilized'inany desired man- Der.

The action of the circuit shown in Fig. 3 may be explained in stillanother manner. In fact, there is disposed between the audio amplifier,or other utilizing means, and the audio frequency amplifier output twodetector circuits. One of thesecletector circuits is of the usual andconventional type. The other detectorA circuit is exactly the same asthe first detector circuit, but differs therefrom in including in theinput circuit thereof a device for reducing the carrier amplitude.However, it should be observed that in both these detector circuits thesame amount of distortion will occur, although less undistorted signalenergy will be produced in the detector circuit which includes thecarrier amplitude reducing device.

Then, by combining the outputs of the two detector circuits insubtractive fashion, it will be obvious that the distortion effectsproduced in both detector circuits, being equal and opposite, willbalance out, leaving less undistorted signal energy than could beobtained by the use of the usual detector circuit itself. In otherwords, although a certain amount of undistorted signal energy is lost bythis method, yet the distortion currents, such as harmonics and otherextra frequency currents, are eliminated from the detector circuit byproviding a second detecting circuit for balancing out the distortioncurrents. This arrangement is, of course, adapted for use in connectionwith the suppression of harmonics in the output circuit of a detector,rather than for the purpose of increasing carrier amplitude toaccomplish the suppression, or for eliminating disadvantages inherent inreceiving carrier energy with carrier amplitude below normal.

While I have indicated and described several systems for carrying myinvention into effect, it will be apparent to one skilled in the artthat my l invention is by no means limited to the particularorganizations shown and described, but that many modifications may bemade without departing from the scope of my invention as set forth inthe appended claims.

What I claim is:

1. A receiving circuit comprising a radio frequency amplifier, adetector circuit, a carrier frequency oscillator having its inputcircuit coupled to the output of the amplifier and its output circuitcoupled to the input of the detector, the oscillator circuit providing asingle path between said amplifier and said detector both for the sideband energy and the carrier energy, and being so arranged that carrierwave energy is amplified to a greater extent than the side band energy.

2. In combination, a source of signal energy, a radio frequencyamplifier, a detector circuit coupled to the amplifier, a seconddetector circuit having its input coupled to the said amplifier, meansfor combining the outputs of both detector circuits in subtractivemanner, and additional means for reducing the carrierV amplitude in thesecond detector circuit.

3. In a radio receiver, an energy collector adapted to receive modulatedcarrier energy, an amplifier having input and output circuits, the inputcircuit of said amplifier being coupled to said energy collector, adetector and an oscillator each having input and output circuits, saidoscillator being arranged to generate oscillations of carrier frequency,the input circuits of both said detector and oscillator being separatelycoupled tothe output circuit of said amplifier in such manner that bothsaid detector and said oscillator have` impressed upon.themfthe-signai-rriuzfrecarrieriandiits. associated sidev bands, yand:means in ASeidel-uma palithzisuned Ato the carrier forY amplifying thecarrierindependently of the side bands. 5` In a radio receiver, anamplifier, adetector circuit', .a path extending 'fromthe output of saidamplifier to the input of said` detector arranged to pass both theYcarrier and its associated sidebands, said pathincludi'ngan electrondischarge device oscillator Whose input circuit is coupled t'othe-output of .saidamplifer and vWhose output circuit lis-coupled Ytothe input oflsaid detector.

RENE A'. BRADEN.

